1. Field of the Invention:
The present invention relates to an image retrieving apparatus and an image retrieving method. More particularly, the present invention relates to an apparatus for and a method of retrieving an image similar to a predetermined query image out of videos.
2. Description of the Related Art:
Hitherto, in an image retrieving apparatus having a video data base for storing video data, an image retrieving method is adopted in which image data similar to either a predetermined image (it will be hereinafter referred to as a query image) or a predetermined video segment (it will be hereinafter referred to as a query video segment) is retrieved out of image data stored in the video data base.
In one typical method of such image retrieving method, a query image and all frames of videos are compared and the images are sorted in decreasing order according to their similarities. However, in this image retrieving method, too much images are presented as candidates, and therefore it takes a long time to implement image retrieval.
Thus, in Laid-open Japanese Patent Publication No. 11-259061, a different method has been disclosed in which a change in an image scene usually referred to as a scene-change is preliminarily detected out of the stored videos, and only every one frame immediately after the scene-change are stored as representative frames. Then, retrieval process is implemented to retrieve a similar image only out of the stored representative scenes instead of entire frames involved in video data.
However, the image retrieving method according to the prior art must encounter many problems as described below.
Namely, in the method of proposing image data nominated according to a lower to higher similarity by comparing a query image with all frames of a video, since the video is a set of frames continuing in time, the continuing respective frames, in general, are quite similar to one another in their contents. Thus, the continuous frames involved in a certain shot are eventually nominated and presented, and accordingly the number of nominated and presented images increases, while causing a problem of necessitating a lot of time for completion of retrieval of an image.
In the method disclosed in the Laid-open Japanese Patent Publication No. 11-259061, retrieval of a query image is implemented to retrieve it out of only a part of frames such as frame images obtained by the detection of scene-change, and therefore frames contained within a scene are not retrieved. Thus, retrieval cannot be implemented with every frame unit. At this stage, if a certain scene contains quite a lot of motion activity, there might be a case where the content of the first frame in a scene is greatly different from those of the respective frames within the scene. In this case, a problem might occur in which a desired frame is not included in the representative frames, which are subjected to retrieving process.
On the other hand, from the time of detection of a scene-change, it may be possible to implement further retrieving of a query image out of the respective frames within the scene. Nevertheless, if it fails to detect a scene-change of a scene containing therein a desired image, the desired image cannot be included in the subject of retrieving, and as a result, retrieving of the desired image cannot be eventually implemented.